In ink-jet printing methods, droplets of ink are directly projected onto a printing medium from very fine nozzles and allowed to adhere to the printing medium to form characters or images thereon. The ink-jet printing methods have now been extensively employed not only in printing applications for ordinary consumers but also recently in commercial and industrial printing applications because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the printing medium, non-contact with printed characters or images, etc.
In the commercial and industrial printing applications, there has been proposed the high-speed printing method in which a rolled synthetic resin film is scanned using a stationary printing head of a line printing type.
Since the synthetic resin films are incapable of absorbing an ink therein, the ink printed on the films tends to still exhibit high flowability even after droplets of the ink are impacted onto the films, and tends to suffer from occurrence of intercolor bleeding and deterioration in quality of characters or images printed thereon. For this reason, in order to efficiently dry the ink printed on the films and prevent occurrence of intercolor bleeding, ink-jet printing methods using a drying means capable of heating a portion of the printing medium which is located just below an inkjet printing head have been proposed.
For example, JP 2013-166271A (Patent Literature 1) discloses an ink-jet printing method using a printing apparatus that includes a printing head provided with ink ejection nozzles and a heating means capable of heating a printing medium from a rear side surface of the printing medium opposed to a front side surface thereof on which the nozzles are disposed, said method including the step of drying an ink containing a solvent, a colorant and a resin using the heating means after the ink is impacted on the printing medium.
JP 2014-94495A (Patent Literature 2) discloses an ink-jet printing method including the steps of ejecting a white-based ink from nozzles to print white-based images on a soft packaging film, ejecting color inks from nozzles to allow the color inks to adhere to the white-based images and thereby print color images thereon, and heating the white-based images and color images at a temperature of higher than 40° C., in which the white-based ink contains a white-based coloring material and a urethane-based resin, but contains substantially no alkyl polyols having a boiling point of not lower than 280° C. In Patent Literatures 1 and 2, as is apparent from the figures shown therein, there are used the printing apparatuses that include the heating means capable of heating the printing medium from a rear side surface thereof, in which the heating means is disposed just below the ink-jet printing head.